<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <input type="text" value="张三" placeholder="提示文本">
  <input type="checkbox" class="inp2">

  <select name="" id="">
    <option value="name1">1</option>
    <option value="name2" selected>2</option>
    <option value="name3">3</option>
  </select>

  <button>按钮</button>

  <script>
    const sel = document.querySelector('select option')
    sel.selected = true

    const inp2 = document.querySelector('.inp2')
    inp2.checked = true

    const btn = document.querySelector('button')
    btn.disabled = true

    const inp = document.querySelector('input')
    inp.value = '李四'
    inp.type = 'password'
    inp.placeholder = '请输入姓名'



  </script>

</body>

</html>